This application claims priority on Japanese Patent Application Number 251410/1999, filed Sep. 6, 1999, the entire disclosure of which is incorporated herein by reference.
1. Technical Field of the Invention
The present invention relates to a method and an apparatus for manufacturing a highly airtight, ceramic-based composite member.
2. Prior Art
The thrust chamber of a rocket engine using a propellant such as NTO/N2 H4 and NTO/MMH is required to be capable of operating at a high temperature that provides higher engine performance. For this purpose, niobium alloys with a coating that can operate at a temperature of about 1,500xc2x0 C. have been used conventionally as the chamber material for many rocket engines. However, these materials have such defects as high density, heavy weight, low strength at a high temperature, and short life of coating.
On the other hand, ceramics can resist heat, but are brittle, therefore the ceramic matrix composite (CMC) was developed by reinforcing ceramics with ceramic fibers. In other words, the ceramic matrix composite (CMC) is made of ceramic fibers and ceramic matrix. Normally, a CMC is represented according to its constituents, that is, ceramic fibers/ceramic matrix (for example, SiC/SiC when both constituents are SiC).
A CMC is light in weight and can operate with a high strength at a high temperature, so this material can possibly be applied for the thrust chamber of a rocket engine, as described above, as well as a fuel piping at a high-temperature portions,.turbine blades, combustor, and component parts of after-burner of a jet engine, etc.
However, conventional CMCs were problematic in that airtightness could not be retained and resistance to a heat shock was poor. More explicitly, with a conventional CMC, ceramic fibers were formed into a predetermined shape, and a matrix was created in gaps between fibers by the so-called CVI (Chemical Vapor Infiltration) process, and to completely fill gaps between fibers with the matrix produced in this CVI process, an impractically long time (for instance, more than one year) was required, which was very difficult.
Also, to increase the airtightness of CMC itself, the PIP (Polymer Impregnate and Pyrolysis Method) process in which components made of ceramic fibers are only dipped in a molten material polymer is effective, however, the cycle of impregnating and heating must be repeated many times (for instance, more than 40 times), so efficiency is poor.
In addition, U.S. Pat. No. 05,632,320 disclosed a RTM method (Resin Transfer Molding Method) which is one of pressurized infiltration processes used in PMC (Polymer Matrix Composite) for Polymer matrix infiltration. However the method needs some huge apparatuses such as dies.
The present invention was developed to solve the above-mentioned problems. That is, an object of the invention is to provide a method and an apparatus for manufacturing a ceramic-based composite member that can increase airtightness and can be applied to practical thrust chambers etc., within a short time.
The method and the apparatus for manufacturing a ceramic-based composite member according to the present invention are configured with (a) a CVI infiltration process for forming an SiC matrix phase on the surface of a shaped fiber fabric, (b) a pressurized infiltration process for pressurizing an organic silicon polymer in a pressurizing direction of the fiber fabric during practical use of the fabric and infiltrating the organic silicon polymer into gaps in the aforementioned matrix phase, and (c) a process for heating the fabric at a high temperature.
The method of the present invention is characterized in that after an SiC matrix phase is produced on the surface of a fiber fabric, the fabric is processed in a pressurized infiltration process. The SiC matrix phase can be created by, for example, a CVI process, as a crackless, dense matrix formed around ceramic fibers. Next, an organic silicon polymer is pressurized in the direction of practical operating pressure of the fiber fabric and pressure-infiltrated through a PIP process, thereby the matrix is formed preferentially in gaps in the matrix phase, gaps after the CVI process are filled, and airtightness of the member can be increased.
Because there are microscopic cracks in the matrix created by the PIP process, bonding forces between ceramic fibers are weak. Therefore, as disclosed in the Japanese patent application No. 019416/1999 (unpublished), as the member is subjected to the PIP process in addition to the CVI process, the modulus of elasticity can be reduced more than that of a conventional CMC produced only by the CVI process, so thermal stresses are reduced and resistance to thermal shock can be greatly improved, as verified through experiments.
According to preferred embodiments of the present invention, the member is maintained for a predetermined time at such a pressure that the organic silicon polymer leaks through gaps in the matrix phase during the aforementioned pressurized infiltration process; next, the member is subjected to a heating process, and furthermore, these pressurized infiltration process and heating process are cyclically applied until satisfactory airtightness of the member is achieved.
In this way, a matrix is formed preferentially in gaps penetrating the composite member, and airtightness can be increased in a short period.
The above-mentioned pressurized infiltration process should preferably be carried out after the matrix is infiltrated by CVI to prevent oxidation, however, the process can be applied at any time provided the interface coating has already been completed.
The present invention offers an apparatus for manufacturing a ceramic-based composite member, provided with holding device (12) for holding a fiber fabric (11) with an SiC matrix phase formed on its surface, airtightly, pressurizing feeder (14) that pressurizes an organic silicon polymer (8) in the direction of applying pressure during use of the fiber fabric and feeds the polymer, and degassing device (16) that removes part of the polymer containing gas bubbles from the organic silicon polymer fed.
In this configuration according to the invention, the fiber fabric (11) with the SiC matrix phase formed on the surface using holding device (12) is kept water-tight, and the organic silicon polymer (8) is pressurized in the direction of pressurizing the fiber fabric during use, and is fed, therefore, by adjusting the pressure the organic silicon polymer can be fed into the fiber fabric at a substantially uniform pressure. In addition, because the organic silicon polymer can be pressurized in the direction of the operating pressure of the fabric and infiltrated into the fabric under pressure, the matrix is created preferentially in gaps in the matrix phase, so that gaps remaining after CVI and PIP processes can be filled, thus the airtightness of the fabric can be increased. Furthermore, degassing device (16) can remove the part of the organic silicon polymer that contains a lot of gas bubbles, and as a result, the uniform organic silicon polymer without bubbles contained can be fed preferentially into gaps in the matrix phase, and a highly airtight matrix can be produced.